Rocker arm assemblies are utilized in internal combustion engines for alternately actuating intake and exhaust valves. As an engine cam shaft rotates, a push rod is selectively actuated by cams located on the cam shaft. The push rods, in turn, direct an upward force on one end of a rocker arm to cause the rocker arm to pivot about a mounting shaft. As the rocker arm pivots, its opposite end generates a downward force to selectively open an intake or exhaust engine valve.
Typically, rocker arms are integral, one-piece parts having a generally U-shaped cross-section including a pair of opposing side walls separated by a bottom wall and a pair of end walls disposed between the side walls. Rocker arms are conventionally either stamped or cast. The above described U-shaped rocker arms are commonly referred to as "boat-type" rocker arms. U-shaped rocker arms generally have adequate stiffness. However, the increased mass and width of U-shaped rocker arms negatively affects the moment of inertia, which is important for engine components reciprocating at very high frequencies. Increased mass also decreases vehicle fuel efficiency. Some other disadvantages of U-shaped rocker arms include loud operating noise, vibration, and undesirable levels of friction.
Lubrication in conventional U-shaped rocker arm assemblies is provided through hollow push rods that channel lubricant up to a lubricant aperture in one end of an adjacent rocker arm. Then lubricant flows onto the bottom wall in between the side walls of the rocker arm.
The previously known rocker arm assemblies include variations having so-called "frictionless" bearings and assemblies without bearings. However, none of the prior known devices allow a bearingless rocker arm shaft assembly to be interchanged with a frictionless bearing rocker arm shaft assembly within the same basic engine design configuration. The incompatibility of the prior art decreases engine manufacturer flexibility by forcing a selection between the higher costs associated with multiple engine design configurations or only being able to offer a single engine design with only one type of rocker arm s haft assembly.
Further, the prior art rocker arm designs lack the ability to have a rocker arm supplier provide a fully pre-assembled rocker arm shaft assembly that can be shipped to and installed at the engine manufacturer's assembly plant. Instead, the prior art designs require the engine manufacturer to pre-assemble the components. Thus, the prior art designs are more susceptible to having loose, individual component parts lost during shipping and handling. Moreover, the prior art designs increase inventory burden on the engine manufacturer and often result in inadequate rotation of parts in inventory.